The present invention relates to a method of determining the quantity of a dihydric phenol in an analytical sample. In particular, the invention relates to a rapid method for the quantitation of a dihydric phenol in the presence of a monohydric phenol.
Dihydric phenols are commercially important compounds used in the synthesis of polycarbonates, polyestercarbonates, polyesters, polyether sulfones, polyimides, and epoxides, among other polymers. Synthetic approaches to dihydric phenols include the catalyzed reaction of two equivalents of a monohydric phenol with one equivalent of a ketone to form the desired dihydric phenol and water; for example, the reaction of phenol with acetone to form 2,2-bis(4-hydroxyphenyl)propane (hereinafter xe2x80x9cbisphenol Axe2x80x9d) is illustrated in the scheme below. 
Alternative syntheses include those substituting other carbon precursors, such as a geminal bis(acetoxy)alkane, for the ketone. These and other synthetic approaches are described, for example, in U.S. Pat. No. 1,977,627 to Greenhalgh, U.S. Pat. No. 2,359,242 to Perkins et al., U.S. Pat. No. 2,623,908 to Stoesser et al., U.S. Pat. No. 3,242,219 to Farnham et al., U.S. Pat. No. 3,394,089 to McNutt et al., U.S. Pat. No. 4,163,116 to Hedges et al., U.S. Pat. No. 4,201,878 to Mark et al., and U.S. Pat. Nos. 5,723,689 and 5,990,362 to Pressman et al.
All of the above described methods have in common the use of a monohydric phenol as a starting material to synthesize a dihydric phenol. This presents a challenge for quantitation of the dihydric phenol in the synthesis reaction mixture. Given their structural similarity, it is not surprising that monohydric and dihydric phenols have similar spectroscopic characteristics. For this reason, the progress of a dihydric phenol synthesis has typically been monitored by a liquid chromatographic method in which the dihydric phenol is separated from the monohydric phenol on an absorption column before quantitation by a method such as ultraviolet (UV) light absorption. Another method could be the use of gas chromatography or gas chromatography-mass spectrometry. Both of these methods require longer time per sample due to the separation phase and the time required to return the separation column to the initial conditions. While such methods enable the accurate quantitation of a dihydric phenol in the presence of a monohydric phenol, they usually require several minutes per sample.
Continuing efforts to discover new catalysts and reaction conditions for the synthesis of dihydric phenols may utilize combinatorial chemistry methods that generate many samples in a short period of time. Known methods for the quantitation of dihydric phenol in combinatorial samples are too slow to be practical for the analysis of the many samples constituting a combinatorial library of reaction conditions. There is therefore a need for a rapid method of quantifying a dihydric phenol in the presence of a monohydric phenol.
The above-described and other drawbacks and disadvantages of the prior art are alleviated by an analytical method, comprising:
injecting into a flow analysis system a known volume of each of a plurality of analytical samples, each sample comprising a dihydric phenol and a monohydric phenol;
detecting the absorbance of the known volume of each analytical sample at at least two wavelength ranges; and
determining the concentration of the dihydric phenol in each analytical sample based on the absorbance of the known volume of each analytical sample at at least two wavelength ranges;
wherein the method has a total analysis time not greater than about 5 minutes per sample.